Apparatus for measuring mechanical parameters of the prostate and for imaging the prostate using such parameters

ABSTRACT

A pressure force sensing array is used to measure the surface stress pattern on soft tissues. The pattern of mechanical stress and the changes in the pattern as a function of the applied pressure, position of the array and time are processed to construct an image of the internal structure of the tissues. The detected parameters and processed image provide information useful in the detection and diagnosis of soft tissue pathologies such as breast and prostate tumors. The present invention relates to an apparatus particularly useful for mechanical imaging of the prostate which comprises a transrectal probe. The probe includes a probe shaft, a position sensor for determining the position of the tip and an array of force sensors for determining the pattern of pressure from tissue deformed by the tip.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Pat. application Ser.No. 08/607,645 filed Feb. 27, 1996 which is a continuation-in-part ofU.S. Pat. application Ser. No. 07/994,109 filed Dec. 21, 1992 and issuedas U.S. Pat. No. 5,524,636 on Jun. 11, 1996. The full disclosures ofboth applications and the issued patent are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus for measuring geometrical andmechanical parameters of the prostate and for imaging the prostate basedupon such parameters

DESCRIPTION OF THE PRIOR ART

Diagnosing early formation of tumors, particularly those caused bycancer, has been a problem that has been attempted to be solved usingvarious techniques, such as ultrasonic imaging, nuclear magneticresonance imaging, x-rays, and the like.

One of the safest and oldest techniques of detecting diseased tissue ispalpation (digital examination). Palpation, that is, examination usingthe sense of touch, is based on he significant differences in elasticityof normal tissues and certain lesions. Palpation has been a commonlyused technique for detecting prostate and breast cancer. Several authorshave proposed various types of devices mimicking palpation to detecttumors using different types of pressure sensors. For example, Frei etal, U.S. Pat. No 4,250,894, have proposed an instrument for breastexamination that uses a plurality of spaced piezoelectric strips whichare pressed to the body being examined by a pressure member whichapplies a given periodic or steady stress to the tissue beneath thestrips.

A different principle for evaluating the pattern of pressuredistribution over compressed breast was proposed by Gentle (Gentle CR,Mammobarography: -a possible method of mass breast screening. J. Biomed.Eng. 10, 124-126, 1988). The pressure distribution is monitoredoptically by using the principle of frustrated total internal reflectionto generate a brightness distribution. Using this technique, referred toas "mammobarography," simulated lumps in breast prostheses have beendetected down to a diameter of 6 mm. According to Gentle, this techniquecan be used for mass breast screening; however, no quantitative data onlumps in a real breast was ever published. The failure has beenexplained by the insufficient sensitivity of the registration system. Itshould be noted, that most of the development of pressure sensors formedical applications has been done not for mimicking palpation but formonitoring blood pressure and analyzing propagation of pulse waves inblood vessels (See, for example, U.S. Pat. Nos. 4,423,738; 4,799,491;4,802,488; 4,860,761).

Another approach to evaluate elasticity of the tissues uses indirectmeans, such as conventional imaging modalities (ultrasound or MRI) whichare capable of detecting motion of a tissue subjected to an externalforce. One approach attempts to determine the relative stiffness orelasticity of tissue by applying ultrasound imaging techniques whilevibrating the tissue at low frequencies. See, e.g., K. J. Parker et al,U.S. Pat. No. 5,099,848; R. M. Lerner et al., Sono-Elasticity: MedicalElasticity Images Derived From Ultrasound Signals in MechanicallyVibrated Targets, Acoustical Imaging, Vol. 16, 317 (1988); T. A.Krouskop et al., A Pulsed Doppler Ultrasonic System for MakingNon-Invasive Measurement of Mechanical Properties of Soft Tissue, 24 J.Rehab. Res. Dev. Vol. 24, 1 (1987); Y. Yamakoshi et al., UltrasonicImaging of Internal Vibration of Soft Tissue Under Forced Vibration,IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control,Vol. 7, No. 2, Page 45 (1990).

Another method proposed for measuring and imaging tissue elasticity isdescribed in Ophir et al., U.S. Pat. Nos. 5,107,837, 5,293,870,5,143,070 and 5,178,147. This method includes emitting ultrasonic wavesalong a path into the tissue and detecting an echo sequence resultingfrom the ultrasonic wave pulse. The tissue is then compressed (oralternatively decompressed from a compressed state) along the path andduring such compression, a second pulse of ultrasonic waves is sentalong the path into the tissue. The second echo sequence resulting fromthe second ultrasonic wave pulse is detected and then the differentialdisplacement of selected echo segments of the first and second echosequences are measured. A selected echo segment of the echo sequence,i.e., reflected RF signal, corresponds to a particular echo sourcewithin the tissue along the beam axis of the transducer. Time shifts inthe echo segment are examined to measure compressibilities of the tissueregions.

Sarvazyan et al., have developed a device for elasticity imaging of theprostate using an ultrasonic transrectal probe (U.S. Pat. No.5,265,612). This device enables physicians to quantitatively andobjectively characterize elasticity moduli of prostate tissues. Theelasticity characterization and imaging is achieved by evaluating thepattern of the internal strain in the prostate and surrounding tissuesusing conventional transrectal ultrasonography. The pattern of internalstrain is obtained by ultrasonically imaging the prostate at two levelsof its deformation. The deformation is provided by changing the pressurein the fluid filling the sheath surrounding the transrectal probe. Inaddition to elasticity, other tumor parameters reflecting the stage ofits development include the geometrical parameters of the tumor, such asits volume or diameter. Lacoste et al., U.S. Pat. No. 5,178,148, havedisclosed a method of determining the volume of a tumor or gland,particularly the prostate, using an endocavity detector probe, inparticular, a transrectal probe.

SUMMARY OF THE INVENTION

New methods and devices for measuring geometrical and mechanicalparameters of body tissues and providing mechanical imaging (MI) of thetissues based on these parameters are described in applicant's parentU.S. Pat. application Ser. No. 08/607,645 and 07/994,109. In essence, apressure sensing array is used to measure the surface stress pattern onsoft tissues, and the pattern of mechanical stress and the changes inthe pattern as a function of the applied pressure, the position of thearray and time are processed to construct an image of the internalstructure of the tissues. The detected parameters and processed imageprovide sensitive information useful in the detection and diagnosis ofsoft tissue pathologies such and breast and prostate tumors.

In accordance with the present invention, apparatus particularly usefulfor mechanical imaging of the prostate comprises a transrectal probeincluding a probe shaft, a tip moveable in relation to the shaft, aposition sensor for determining the position of the tip and an array ofpressure sensors for determining the pattern of pressure from tissuedeformed by the moveable tip. Signals indicaive of the position of thetip and the pattern of pressure can be provided to a processor formechanical imaging.

In a preferred embodiment, the apparatus comprises a control handle, aprobe shaft and the moveable tip. The tip is moveable in an upward anddownward direction. The handle advantageously includes a control leverfor controlling tip movement via a control rod and a locking mechanismfor locking the tip at a predetermined position. The handle can includea switch, such as a control button, for controlling a computer.Preferably the outer surfaces of the probe are covered with a soft, thinflexible rubber sheath to permit transmission of pressure to thesensors. The probe can be composed largely of plastic materials for easeof maneuverability and biocompatibility.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, advantages and various additional features of the inventionwill appear more fully upon consideration of the illustrativeembodiments now to be described in detail in connection with theaccompanying drawings. In the drawings:

FIG. 1 is a schematic representation of a model of soft "tissue"illustrating a device for loading incorporating pressure sensors used inthe present invention;

FIG. 2 is the device of FIG. 1 after loading the tissue, andillustrating a typical pressure curve across a surface of the tissue;

FIG. 3 is similar to the tissue compression in FIG. 2, illustrating theeffect of a presence of a tumor in the tissue;

FIG. 4 is an illustration of the structure shown in FIG. 3, with apiston deforming tissue from a side opposite from the pressure plate;

FIG. 5 is a schematic illustration of loading parameters for a modeltissue being examined and a tumor in such tissue; differential pressureratio;

FIG. 5A is a plot of calculated differential pressure ratio across thesurface at differing ratios of moduli of elasticity ratio betweensurrounding tissue and a tumor;

FIG. 6 is a graphical representation of the calculated relationshipbetween differential pressure ratio and moduli of elasticity ratios fora loading structure shown in FIG. 5;

FIG. 7 is a schematic representation similar to that shown in FIG. 5with certain loading parameters illustrated;

FIG. 7A is a graphical representation of the calculated differentialpressure ratio across the surface at differing depths of a tumor intissue shown at FIG. 7;

FIG. 8 is a graphical representation of calculated differential pressureratio relative to the diameter of a tumor being sensed at differingdepth of the tumor as shown in FIG. 5;

FIG. 9 is a graphical representation of the calculated differentialpressure ratio relative to the diameter of a tumor, at differing ratiosof moduli of elasticity between the surrounding tissue and the tumor;

FIG. 10A is a side sectional view of a transrectal probe in accordancewith the present invention;

FIG. 10B is a detail view of a pistol grip handle for a transrectalprobe in accordance with the present invention;

FIG. 10C is the top view of an articulated probe tip;

FIGS. 11A-C are detail views of the probe tip showing a pressure sensorarray and a position/orientation sensor;

FIGS. 12A-C are detail views of the probe joint which permitsarticulation of the probe tip;

FIG. 13 is a schematic diagram of the method and apparatus in accordancewith the present invention;

FIG. 14A is a sectional view showing the relationship of the probe,rectal wall, and prostate with internal nodule;

FIG. 14B is a schematic diagram showing virtual lines of equal pressurecalculated from the data obtained using the position sensor and pressuresensor array of the present invention;

FIG. 15A is a side sectional view of an alternate embodiment of atransrectal probe in accordance with the teachings of the presentinvention;

FIG. 15B is a top view of the transrectal probe shown in FIG. 15Aincluding a sheath;

FIG. 15C is a top view of the transrectal probe shown in FIG. 15A foruse by a right-handed user;

FIG. 15D is a top of the transrectal probe for use by a left-handeduser;

FIG. 16A and 16B are side and bottom views of a preferred moveable tipfor the probe of FIG. 15A;

FIG. 17 is a cross section of the tip of FIG. 16A, showing a preferredsensor arrangement;

FIG. 18 is a schematic circuit diagram showing the signal paths from theprobe sensors;

FIG. 19 is a schematic flow diagram of the data acquisition steps inimaging a prostate;

FIGS. 20A-20F illustrate computer displays during steps of the preferredembodiment of the method; and

FIG. 21 is a chart showing the flow of data in the preferred imagingprocess.

It is to be understood that the drawings are for purposes ofillustrating the concepts of the invention and, except for the graphs,are not to scale.

DETAILED DESCRIPTION OF THE INVENTION

This disclosure is divided into two parts. Part I describes severalembodiments of the transrectal probes particularly useful for measuringgeometrical and mechanical parameters of the prostate, and Part IIdescribes the use of the probe and the parameters it acquires to providea mechanical image of the prostate.

I. Probes For Measuring Geometrical and Mechanical Parameters of theProstate

Referring to the drawings, FIGS. 15A-D illustrate a preferred embodimentof a transrectal probe for measuring geometrical and mechanicalparameters of the prostate. In essence, the probe 300 comprises acontrol handle 307, such as a pistol grip handle, a probe shaft 306,such as a rigid tube, extending along an axis from the handle, and amoveable tip 301 including an array of pressure sensors 302 on the tipsurface 303 and a position/orientation sensor 304 for measuring theposition of tip 301. The tip is moveable above and below the axis of theshaft. In its axial position, the tip can measure pressure from surfacesof the prostate parallel to the axis. When tilted above the axis, thetip can measure pressure from rising surfaces of the prostate, and whentilted below the axis, it can measure falling surfaces of the gland.

Moveable tip 301 is coupled at axis 305 to rigid tube 306. Rigid tube306 is attached to pistol grip handle 307. Rigid rod 308 is positionedwithin rigid tube 306. End 309 of rigid rod 308 is coupled to moveabletip 301 and end 310 of rigid rod 308 is coupled to probe tip controllever 311. Probe tip control lever 311 can be depressed and released formoving moveable tip 301 by rigid rod 308 in an upward vertical direction312 or in a downward vertical direction 313, allowing moveable tip 301to be articulated over angles in the range of ±45 .

Lever button 314 can lock the tip angle. End 315 of lever 311 isattached to end 310 of rigid rod 308. Locking rod 317 is formed on leverbutton 314. Releasing the lever button 314 positions end 318 of lockingrod 317 in one of a plurality of depressions 319 formed in pistol griphandle 307, thereby locking moveable tip 301 at a predeterminedposition. Thereafter, lever button 314 can be depressed again to releasemoveable tip 301.

The position/orientation sensor can be a 3SPACE® Inside Trak™ sensingelement made by Pohlemus Inc. It will be appreciated that other positionsensors known in the art can also be used.

Switch 320 is used for controlling interactions with computer interface322. Switch 320 is positioned within pistol grip handle 307. Controlbutton 321 is coupled to switch 320. Control button 321 can be depressedat various stages during use for controlling input from pressure sensor302 and position orientation sensor 304 to computer interface 322through cable 323. For example, control button 321 can be depressed atthe beginning and end of an examination session.

Sheath 324 covers a portion of rigid tube 306 and moveable tip 301 forpreventing damage to moveable tip 301, as shown in FIG. 15B. Sheathslippage guard ribs 325 can be positioned along rigid tube 306. Sheath324 is held by sheath slippage guard ribs 325 to rigid tube 306.Preferably, sheath 324 is formed of a latex material. Disposable sheath326 can be placed over sheath 324 to cover entire moveable tip 301. Forexample, disposable sheath 326 can be a conventional condom. Disposablesheath 326 can be retained on rigid tube 306 with rubber ring 327.

FIG. 15C illustrates a top view of probe 300 for transrectal mechanicalimaging by a right-handed user of probe 300 with horizontal movement inthe direction of arrows 331 and 332. Pressure sensors 302 are positionedon left surface 303 of moveable tip 301 for simulating the movement of afinger tip of a right-handed user of probe 300. FIG. 15D illustrates atop view of an embodiment of probe 300 for transrectal mechanicalimaging by a left-handed user of probe 300. Pressure sensors 302 arepositioned on right surface 334 of moveable tip 301 for simulating themovement of a finger tip of a left-handed user of probe 300.

Probe 300 can be used for examination of the prostate in two differentpositions. In the first position, the patient to be examined is in akneeling position with their face in a downward position. The prostateis positioned below probe 300. In the second position, the patient to beexamined is in a jackknife position laying on their side. When thepatient is laying on their right side, the prostate is positioned on theleft side of the patient's rectum. In this position, the embodiment ofthe probe shown in FIG. 15C for a right-handed person is used forexamination. When the patient is laying on their left side, the prostateis positioned on the right side of the patient's rectum. In thisposition, the embodiment of the probe shown in FIG. 15D is used forexamination.

Preferably, rigid tube 306, moveable tip 301 and pistol grip handle 307are formed from plastic FDA grade acetal polymer for biocompatibility.The use of a plastic material also has the advantage of non-interferencewith position/orientation sensors that can be magnetic field sensitive.It will be appreciated that rigid tube 306, moveable tip 301 and pistolgrip handle 307 can also be formed of aluminum and other conventionallight-weight metals. Probe 300 has the advantage of manually controllinga moveable sensing tip without motors or electricity. Probe 300 isformed of a light-weight material for ease in manipulation of the probe.Probe 300 can be used in a similar manner as probe 100 described abovefor mechanical imaging and detecting tumors in the human prostate gland.

FIGS. 16A and 16B are enlarged side and bottom views, respectively ofthe preferred moveable tip 301 showing advantageous locations of thearray of pressure sensors 302 and position/orientation sensor 304. Thetip 301 is connected to the shaft 306 by a hinge 335. Extension of rod308 can thus move the tip 301 below the shaft axis (in the direction ofthe sensors) and retraction can move the tip in the opposite directionabove the shaft axis.

Preferably, the array of pressure sensors are arranged in a left row302a and a right row 302b. Left row 302a measures pressure appliedagainst the left side of tip 301 and right row 302b measures pressureapplied against the right side of tip 301. Left row 302a and right row302b provide feedback to the user of probe 300 to assist in controllingpositioning of probe 300 within the patient. For example, probe 300 canbe manipulated within the patient to be examined in order to provideequal pressure at left row 302a and right row 302b, thereby determiningthe correct position of probe 300 and aiding the user in performing theexamination procedure.

FIG. 17 is a cross section of moveable tip 301 through a pair ofpressure sensors 302 illustrating the preferred pressure sensors whichare advantageously bending beam force sensors. Force applied to sensorregion 302 bends beam portion 336 which is detected by a pair of straingauges 337A, 337B bonded on opposite sides of each beam 336. The tipwalls, sensor regions 302 and beam portions 336 are all preferablyplastic.

FIG. 18 is a schematic circuit diagram showing the original paths fromthe probe sensors to the signal processing circuitry. Signals from eachstrain gauges 337A and 337B pass first to a preamplifier, here asix-channel preamplifier, 338. The amplified signals are applied to amultiplexer 339, and the multiplexer signals are converted to digitalsignals by A/D converter 340 and fed into computer 341 for signalprocessing. The signal from probe switch 320 can be convenientlyprovided to the computer via multiplexer 339. The signals fromposition/orientation sensor 304 are detected by the associated interfacecircuitry 342 and provided directly to the computer.

II. Use of the Probe In Mechanical Imaging of the Prostate

The method for transrectal imaging of the prostate using the presentinvention is based on a new technology of medical imaging described inU.S. Pat. No. 5,524,636, which is incorporated herein by reference. Thismethod is referred to herein as Mechanical Imaging ("MI"). The essenceof MI is the reconstruction of the internal structure of soft bodytissues by measuring a surface stress pattern using a pressure sensingarray. The pattern of mechanical stress and its changes as a function ofapplied pressure and time contain comprehensive information on themechanical properties and geometry of the internal structures of thebody tissues.

The most promising applications of MI devices are in those fields ofmedicine where palpation is proven to be a sensitive tool in detectingand monitoring diseases, including prostate cancer. Palpation, i.e.digital rectal examination (DRE), is currently the most common method ofprostate cancer detection. Despite the obvious usefulness of thediagnostic information obtained by DRE, there are no technical means anddevices capable of yielding data similar to that obtained by the fingerof a skilled examiner. To examine the gland, a physician inserts afinger into the rectum and, feeling the gland through the rectal wall,searches for abnormalities in its size, contour, consistency andlocalization. A hard, nodular, or indurated prostate discovered onroutine DRE may be the first indication of cancer.

The probe in accordance with the present invention in inserted into therectum and manipulated using the handle. The tip applies pressuresimilar to that applied by a human finger. The pressure sensors mountedon the tip measure the localized pressure distribution. Theposition/orientation sensor provided in the tip determines the positionof the tip corresponding to the particular pressure pattern measured bythe pressure sensor array. Signals from the pressure sensor array andposition/orientation sensor are used to calculate a virtual pattern of aproperty such as stress and strain for the examined prostate. Atheoretical geometrical model of the examined prostate is definedassuming that the tissue is homogeneous and has dimensions estimatedfrom the measurement data. Theoretical patterns of stress and strain arethen evaluated using said theoretical geometrical model. The virtualpattern and theoretical pattern of strain or stress are compared anddifferences indicate location and relative hardness of a differingelasticity region. The theoretical geometrical model is then adjusted byvarying the spatial distribution of elasticity to minimize thedifferences. This adjustment of the geometrical and mechanicalparameters of model is iteratively repeated until said differencesbecome less than a preselected level. Thus, an inverse mechanicalproblem is solved and a spatial distribution of elasticity modulus isobtained in the tissue portion being examined. The resultantdistribution is used to construct and display an image of the examinedprostate.

Without being bound by any particular posited theory, the followingconstitutes applicant's belief concerning the theoretical aspects of theinvention. The pressure patterns on the surface of an investigatedtissue portion together with given boundary conditions enable one toreconstruct internal structures in underlying tissue and to evaluaterelative hardness and softness of tissue in localized areas. Therelationship between elasticity differences in localized areas inside oftissue, the stress pattern on the surface of the tissue, and internalstrain pattern permit detecting and quantifying tissue abnormalities.

When calculating the mechanical properties of tissues, calculations arebased on a model of the tissue as being linearly elastic andincompressible media. Such an approach is a first approximation which issufficient to solve all questions arising in mechanical elasticityimaging.

Accordingly, the graphical representations discussed in the detaileddescription of the invention are based on calculations from the generalequations presented below. The following equations are general equationsfor three-dimensional linear theory of elasticity for in-compressiblemedia like tissues or another water based system, that is a systemhaving a Poisson s ratio of 0.5 (Sarvazyan et al., Biophysical Bases ofElasticity Imaging, Acoustical Imaging, Vol. 21, 223, 1995).

The equations for dynamic equilibrium are: ##EQU1## where:

U, V, W are components of displacement;

ρ is density of media; and

σ_(ij) are components of stress tensor.

The pattern of stresses must be related to a pattern of strain. Thisrelationship for incompressible media (e.g. tissues or other water basedsystems) is given by the following equations. ##EQU2## where ##EQU3##where v=0.5 is the Poisson ratio, E is the Young's Modulus and ##EQU4##

By combining equations (1) and (2), we can obtain three equationscontaining only three unknowns, U, V, W, which are components ofdisplacement plus the unknown pressure P.

An additional equation is the equation of incompressibility showing thatdivergence of vector of displacement equals zero: ##EQU5##

Equation (3) represents the condition that when force is applied to thesoft tissue, all the deformation of tissue is related to changes of theshape of the soft tissue but not the volume, because Poison s ratio is0.5, that is the bulk compressional modulus of soft biological tissuesis many orders of magnitude higher then the shear elasticity modulus.

The mechanical characteristics of tissue involve not only elasticity asdiscussed, but also viscosity. Thus, the tissue is a viscoelasticmaterial that requires description in both viscous and elasticcomponents. Viscosity affects the information received because with aviscoelastic material, there is a time delay between force applicationand any displacement that occurs. In a dynamic mode where force isapplied in time, the development of stresses in time provides theinformation on viscosity.

In case of viscoelastic media, the components of the stress tensor inequation (2) should have following additional terms for shear viscosity,μ^(*) ##EQU6##

The shear modulus and Young's modulus of soft tissue are different by afactor of 3, because Poisson s ratio is 0.5. While either modulus can beused for examination of the tissue, Young's modulus is used in thedescription of the present invention.

In the case of harmonic disturbances, temporal dependence can be easilyremoved from these equations and the system of the differentialequations for amplitudes will be obtained.

FIG. 1 illustrates a portion of a soft tissue 10 that is supported on abase 11 which supports a flat rigid plate 12 capable of exertingpressure thereon from a force generator 13. A series of individualpressure sensors indicated at 15 are provided on the bottom surface ofthe plate 12 to sense pressure in an array across the surface of tissue10.

FIG. 2 represents a pressure profile P(x) of the homogeneous tissue 10when deformed. FIG. 3 illustrates a homogeneous tissue pressure profilein the dotted line and the profile of tissue 10 having an inclusion 18in the solid line. The difference between these two pressure profilesshown in FIG. 3 provides information on the presence, location, andrelative elasticity of inclusion 18 with respect to surrounding tissue10. The strain pattern on the surface of the tissue 10 as shown in FIG.3 is in this case represented in the form of pressure profile P(x). Thisstrain pattern depends on the presence of an inclusion 18, as well as onthe dimension of the tissue 10, neighboring anatomical features of thattissue, such as presence of a bone, and on the geometrical relationshipof the tissue 10, support member 11 and deformation member 12.Therefore, the difference between the measured profile P(x) and theprofile P_(o) (x), shown by the dotted line, theoretically calculatedfor a homogenous model of that tissue under same boundary conditions,contains direct information on the inclusion, rather than the strainprofile P(x) itself.

FIG. 4 schematically illustrates how the present invention enhances theamplitude of the pressure profile and, thus, improves detection of aninclusion. In this instance, the tissue 10 is supported on a base 11,and a schematically shown piston or block 24 which also is called a"finger" as used in palpation, is provided on the base and is caused toprotrude into the tissue and compress the tissue in a localized areaindicated at 26 directly below inclusion 18, which can be a tumor.

The represented pressure profile schematically disposed on the top ofthe pressure plate 12 (which is displaced the same as that previouslyexplained) represents the data provided by the pressure sensors 15. P(x)is represented as a dashed line and is the profile substantially as thatshown in FIG. 3. P*(x), indicated by line 28, represents the pressureprofile resulting from the presence of the piston 24 directly under thetumor. The piston 24 acts like a probe to cause extra compression in thedesired region (e.g., inclusion 18) in addition to the generalcompression of the tissue 10 between plate 12 and base 11. This resultsin a substantial increase in the pressure profile P*(x) which reaches amaximum at P*_(max) directly over the tumor. By comparing the respectivepressure profiles P(x) and P*(x), one can recognize that a much greateramplitude of the pressure profile can be obtained from the pressuresensors (to indicate an abnormality) when a probe (e.g., piston 24) orother extra compressive force is directed in the region of a tumor. Inthis case, a change in the pressure profile amplitude because of thepiston 24 is represented as ΔP*=P*-P.

FIGS. 5-9 are schematic examples to illustrate the applicability of thetheory to the methods and devices disclosed, and to show the range ofvariables and measured parameters available for calculating meaningfulvalues for quantitative analysis and evaluation. The illustrations oftissue are not meant to represent any particular portion of a humanbody.

In FIG. 5, a schematic representation illustrates tissue having a tumortherein of a certain size and location. The graph of FIG. 5A illustratesa particular calculated differential pressure ratio as a function of thedistance along the horizontal axis on the surface of the tissue. Thegraph is based on the dimensions shown in FIG. 5 having certain values,such as those listed in FIG. 5A. The symbol (E) represents theelasticity modulus (Young's modulus) of the tumor and (E_(o)) representsthe elasticity modulus (Young's modulus) of the surrounding tissue. Aratio of these two moduli of elasticity (E/E_(o)) provides an indicationof the hardness of the tumor relative to the surrounding tissue.

It is known that the Young s or shear elasticity modulus of a tumorvaries significantly from the modulus of elasticity for surroundingtissue. For example, carcinoma may have an elasticity modulus of 10times the elasticity modulus of normal tissue. However, in some cases,the elasticity modulus of tumors may not be substantially different fromthat of normal tissue making the tumors "nonpalpable". FIGS. 5 and 5Aillustrate that the differential pressure profile ratio, namely(ΔP/P_(o)), (a change in amplitude of the pressure sensed at aninclusion divided by the pressure in that region of normal tissue) inthe region surrounding the tumor is quite sensitive to changes in theelasticity modulus ratio (E/E_(o)).

In FIG. 5, a "block" of tissue 10 has a height H from a base to thecontact point with the pressure sensors 15, and has a length L extendingalong the "X" direction (i.e., horizontal axis). A tumor 30 ispositioned in the tissue 10, and is located a distance below the loadingplate 12 equal to (h) and it has a diameter (d). Tumor 30 is locatedalong the horizontal axis at a distance (a) from a left edge of thetissue 10.

FIG. 5A is a graph illustrating the differential pressure ratio(ΔP/P_(o)) (values shown on the vertical axis), as a function of thedistance along the X axis from the left edge of the tissue 10 to theright. The position of the tumor 30 at (a) is indicated by a verticaldotted line in FIG. 5A. Several plots of (ΔP/P_(o)) as a function of(X/L) are shown, each corresponding to a given ratio of moduli ofelasticity (E/E_(o)), which indicates the relative hardness between atumor and normal tissue.

With the parameters having the values shown in FIG. 5A, the plotsillustrate that a tumor/tissue combination having an elasticity moduliratio (E/E_(o)) of only 1.5, i.e., the tumor having a modulus ofelasticity of 1.5 times that of the surrounding tissue, a detectablechange in the pressure signal of about 3% is observed for the regionsurrounding the tumor. This means that even tumors that are not muchharder than surrounding tissue can be detected quite easily. It is knownthat a tumor in a breast, for example, can be detected by a palpation(which is the only technique available for evaluating elasticity), butpalpation is reliable only when the tumor has progressed so its Young'smodulus is more than five to ten times larger than that of surroundingtissue. The differential pressure signal (ΔP/P_(o)) shows a morepronounced effect near the tumor when the elasticity moduli ratio(E/E_(o)) is 2 or 5 or more. However, in this case when the elasticitymoduli ratio is greater than 7.5 (e.g., 10), there is not a substantialincrease in the differential pressure profile above that shown forE/E_(o) =7.5.

When tumors or inclusions are softer than the surrounding tissue, e.g.,the ratio (E/E_(o)) is 0.5, a substantial difference in the differentialpressure profile (ΔP/P_(o)) in the region of the tumor is readilyobservable. A more pronounced effect occurs when the ratio (E/E_(o)) is0.25. Accordingly, by observing a relatively small change in thepressure profile (only 2-10%), one can detect tumors that have arelatively small change in the modulus of elasticity. This clinicallysignificant data is obtained by using a pressure sensor array extendingacross the surface of the tissue and external to the tissue thatmeasures a pressure profile response during compression of the tissue.

FIG. 6 illustrates the changes in pressure sensed as a function of thechange in the elasticity modulus ratio (E/E_(o)).

Similar to the illustration in FIGS. 5 and 5A, FIG. 6 shows that easilyachievable resolution of a few percent in the pressure profile ratio(ΔP/P_(o)) can enable one to detect inclusions differing from thesurrounding tissue in hardness to an extent which does not permitpalpatory detection. The graph is based on a tissue block 10 having theparameters such as indicated on FIG. 6. The values on the horizontalaxis (E/E_(o)) are provided on a logarithmic basis to facilitatecomparison purposes.

FIGS. 7 and 7A illustrate that the capability to detect a tumor within ablock of tissue depends on the distance of the tumor from the tissuesurface (skin) and pressure sensors. As seen in FIG. 7, the block oftissue 10 has a tumor 30 located therein and, in this instance, thevertical height of the tumor is represented as d₁ and the lateral widthof tumor is represented as d₂. The parameter (a) represents the tumor'sdistance from its position from the left side of the tissue block. A setof values for the dimensions shown in FIG. 7 are listed in FIG. 7A. FIG.7A shows the calculated plot of the pressure profile ratio (ΔP/P_(o))(the change in pressure of tumor tissue relative to normal tissuedivided by the pressure sensed with no tumor) as a function of (X/L)along the X axis. This graph illustrates that a substantial change inthe pressure profile ratio (ΔP/P_(o)) of about 0.3 is observed when thetumor is a small distance (h=5 or 10 mm) from the tissue surface andthat a smaller change in pressure profile ratio occurs when the tumor isfar from the surface (e.g., h=30 mm). However, even when the tumor isdeep (h=30 mm), the pressure profile ratio change is still readilydiscernible (with (P/P_(o) about 0.1 which is quite measurable) toindicate a tissue abnormality at about X/L=0.70. The ratio of (E/E_(o))is taken to be equal to 2.

FIG. 8 illustrates the effect on the ability to ascertain a change inpressure with the sensors 15 as a function of the change in the diameterd of the tumor 30. As seen in FIG. 8, the elasticity moduli ratio(E/E_(o)) is equal to five, and the graph shows a plot of (ΔP/P_(o))versus d for a tumor with h=10 mm (indicated by line 32) and a tumorwith h=20 mm (indicated by line 34). The pressure ratio (ΔP/P_(o)) atthe point of surface above the tumor, is indicated along the verticalaxis, while the diameter of the tumor d is indicated along thehorizontal axis.

The reference line indicated as 35 is more or less the base line forsensitivity of the ratio (ΔP/P_(o)) measurement that can be easilyobtained with existing pressure sensors. An accuracy of about threepercent for pressure sensors is quite achievable, and the base line 35represents a change of about three percent, which will give a clearindication of the presence of a tumor in normal tissue having a diameter(d) in the range of one to two millimeters. FIG. 8 indicates that, thelarger the tumor, the greater is the change in the pressure ratio.

FIG. 9 again illustrates the change in the pressure profile ratio(ΔP/P_(o)) at the point of surface above the tumor as a function of thediameter (d) of the tumor. However, this time, the depth (h) of thetumor below the sensors 15 is set at 10 mm and a plot is provided forthe case when the elasticity moduli ratio (E/E_(o)) equals 5 (indicatedby upper curve 38) and when (E/E_(o)) equals 2 (indicated by lower curve40). As expected, the greater the difference in the elasticity modulusbetween the tumor and surrounding tissue, (a larger ratio (E/E_(o))),the more substantial change in the pressure profile ratio (ΔP/P_(o)) fora given diameter tumor and the more easily the tumor will be detected.Taking the ratio (ΔP/P_(o)) as an indication of sensitivity, one canobserve line (E/E_(o) =5) crossing a threshold level of sensitivity(indicated by the dashed line at 39) indicating that detection of atumor in the range of 1 mm can be made. When an elasticity modulus ratiois 2 (curve 40), one can observe that a tumor of 2.5 mm in diameter (d)could be detected. It is well known that palpation permits detection oftumors only if their diameter is over 8-10 mm, but not smaller. Thegraph in FIG. 9 shows quantitatively how the detection device (pressuresensors) becomes substantially more sensitive (on a relative basis,i.e., a larger change in the pressure profile ratio (ΔP/P_(o)) isobserved) as the elasticity moduli ratio (E/E_(o)) of the tumor tissuerelative to the normal tissue increases.

FIGS. 10A-C, 11A-C, and 12A-C show sectional views and main elements ofan alternative embodiment of the transrectal Mechanical Imaging probe.Referring to the longitudinal view of the probe 100 shown in FIG. 10A,the probe 100 comprises a moveable tip 102 which contains an array ofpressure sensors 101 and a position/orientation sensor 103 (sensingelement of the 3SPACE® INSIDETRAK™ position/orientation tracking devicemade by Polhemus Inc., Colchester, Vt.). The resolution of the 3Dposition measurements achievable with this particular system is 0.1 mm,assuming that the maximum distance between the main electronic unit(fixed outside the probe) and the sensing element 103 (mounted inside ofthe tip 102 of the probe 100) is no more than 50 cm. The tip 102 of theprobe 100 can be made significantly thinner than a finger of aphysician. The tip 102 is mated to a rigid tube 111, which in turn isattached to a pistol grip handle 114. A disposable rubber sheath 113covers the entire tip 102 as well as the tube 111. The electricalconnections for the pressure sensor array as well as the position sensorare carried via a cable 112 (partly shown). A flexible joint between thetip 102 and the tube 111 shown in detail in FIG. 12 is provided to allowthe tip to be articulated over angles ranging from 0 to ±45 vertically,and ±90 horizontally. The joint consists of disks 105 and 107 whichallow vertical motion, and disks 108 and 110 which allow horizontalmotion. Two stepper motors 121 and 122 within the handle drive controlcables 106 and 109, thereby permitting positioning of the probe tip 102,based on operator commands. The probe 102 tip position is controlled bypressing the various buttons on the handle 114, a two-position switchfor up/down 123, 124, and another two-position switch for left/rightoperation 125, 126. In addition to the stepper motors, the handle alsocontains a printed circuit board (PCB) with all electronics necessaryfor operating the motors, as well as a first stage of the dataacquisition circuit. The control cables 106 and 109 are tensioned by tworollers 115 connected to tensioning springs 116. The springs 116 aremounted on a safety switch 117 which is connected to the handle via asafety spring 118. The resistance of the spring 118 is calibrated sothat the forces experienced by the patient can never exceed certain safelimits. The operator can manually release the tension of the cables 106and 109 by pulling on the safety switch 117 if there is any indicationthat the patient is experiencing discomfort or pain. In addition to thismechanical safety mechanism, it also is possible to use a sensor whichwill monitor the tension of the springs 116 and which will stop themotion of the stepper motors 121 and 122 if a preselected level oftension is reached. Alternatively, a biopsy needle (not shown) can beprovided on the probe 100 for taking a tissue sample.

FIGS. 11A-C and 12A-C are detail views of the probe tip and the jointwhich permits articulation of the probe tip. The pressure sensor 101 foruse in the prostate transrectal probe 100 employs a polyvinylidenefluoride (PVDF) piezoelectric film (such as manufactured by AMP Inc.,Valley Forge, Pa.). Other pressure sensors may be used. However, thePVDF film pressure sensors are highly sensitive, easy to work with,provide excellent matching with soft biological tissue and are readilyavailable. There are several ways in which the PVDF film can be mountedon the tip 102 of the transrectal probe 100 to serve as a pressuresensor. In one of the possible patterns of the sensor arrangement (FIG.11C), there are two long 1×12 mm sensors on each side of the array.These are used together with two end sensors in the row of 6 2.5×5 mm toprovide information. This information is displayed to the operator sothat he or she can adjust the position of the sensor during examinationto provide a more even pressure distribution. It can also be used tofilter out those points of the collected data which were obtained withthe array tilted relatively to the surface of the prostate.

FIG. 13 is a schematic diagram showing the processing of signals 200from the probe 100. Pressure sensor data 210 and position/orientationsensor data 220 are combined for calculating the virtual patterns ofstress and strain 230. An ideal geometrical model 240 of the prostate isgenerated from a database 250 and is further adjusted to match theestimated dimensional parameters of the examined prostate. Using thisadjusted geometrical model 260 theoretical patterns of stress and strainare evaluated and compared with the respective virtual stress and strainpatterns, with the differences being used to create a mechanical model270 of the prostate. This mechanical model with addition of relevantdata from the database is used to create and display an image 280.

FIG. 14A shows the relationship of the probe, rectal wall, and aprostate with a nodule in cross section. FIG. 14B illustrates thevirtual lines of equal pressure calculated from the data obtained by theposition sensor and pressure sensor array. Equal pressure lines denotedin FIG. 14B as P=0, P₁, P₂, and P₃ which correspond to different levelsof pressure, are related to the virtual strain profile. A fraction ofthe prostate contour shown in FIG. 14B by the bold dotted line isreconstructed using the equal pressure profile data and the nonlinearityof the strain/stress relationship. At low level of pressures when thecompression is related mainly to the motion of the rectal wall tissuethe system behaves linearly. At a certain level of compression the slopeof the strain/stress curve exhibits sharp increase reflecting theresistance of the prostate tissue. In each region over the prostatethere is a point in the space where the strain/stress relationshipstarts to change sharply its slope. The surface formed by these pointscorresponding to a certain level of nonlinearity of the strain/stressrelationship is determined by the geometrical parameters of the examinedprostate and can be used for estimating the contour of the prostateshown in FIG. 14B by dotted line. The data shown schematically in theFIG. 14B can also be used to evaluate the virtual stress pattern. Thevirtual stress pattern is obtained by calculating the pressure gradientsfor the points on the surface shown by dotted line. Both virtual strainand virtual stress profiles are further used to form a mechanical modelof the examined prostate using additionally relevant information from ageneral database, as shown in FIG. 13. Referring to the drawings, FIG.19 is a schematic flow diagram showing the preferred steps involved dataacquisition. The first step, shown in block A, is to insert the probeinto the rectum to the neighborhood of the prostate and to transmitposition and pressure data from the probe to the processor.

In the preferred embodiment, the processor can display an image oftypical pelvic anatomy and the position of the probe in relation to theanatomy along with a designation of the region to be scanned with theprobe. FIG. 20A shows a representative image with the entering probelocation shown as a white area and the region to be scanned ("bleared")designated by a dashed-line rectangle (a "window" to be cleared).

The next step shown in block B of FIG. 19 is to determine the locationof the prostate in the test subject using position and pressure data andto produce an image of the prostate in relation to the probe.

In the preferred embodiment, the prostate is located by manipulating theprobe to scan the region in the image window. The initial image on thecomputer screen at the beginning of this phase can be a vaguerepresentation of the prostate and pelvic anatomy. This initial imageserves as a map to navigate the probe. A cursor on the screen canrepresent the tip of the examining probe.

The position feedback on the computer screen helps the user adjustmanipulation of the probe. The pressure exerted by the operator and therate of movement of the probe can be indicated on the screen to directand optimize operator performance. The color of the cursor can bechanged to indicate whether the pressure being applied is insufficient,excessive or adequate to optimally image the prostate. If the probe isbeing moved too fast, a warning signal can be placed above the image onthe screen. Similarly, if the probe is misoriented so that less than allthe sensors contact tissue, an appropriate misorientation message can bedisplayed.

The computer display can show the motion of the probe in the window byclarifying the examined part of the initially vague image. FIG. 20Bshows the window nearly cleared with typical features of the region,including the prostate, located relative to the probe. Note that theinstruction to the operator: "Scan the window until clear" is presentedadjacent the image screen.

When the operator clears the window, an "End of task" signal can be sentto the processor by depressing a switch on the probe control handle.Alternatively, the processor can be programmed to recognize that thewindow has been cleared.

Upon clearing of the window, the processor can calculate the position ofthe center and boundaries of the prostate, thereby permitting the imageon the screen to correctly show the relative position of the probe withrespect to the actual prostate. These calculations take about 10-15seconds, after which the image on the screen can zoom out to reveal theprostate and neighboring structures. FIG. 20C illustrates suchtransition zooming, with the prostate shown centered between the pelvicbones. After this enlarged image of the prostate appears on the screenthe process moves into phase 2.

The next step (block C of FIG. 19) involves using the image of theprostate location and the probe to pressure map the prostate andtransmit position and pressure data to the processor.

In the preferred embodiment, the processor program displays a sequentiallist of regions of the prostate to be examined adjacent the imagescreen, and the operator performs this sequence of operations.Advantageously, the choice of this sequence is similar to that of aregular digital rectal examination so that it is familiar to theoperator. After completion of each step of the sequence, the operatorcan send an "End of Task" signal, and the processor can check the taskon the display and highlight the next task in the sequence. FIG. 20Dshows a typical image of the prostate and taskbar.

The fourth step shown in FIG. 19, block D, is to determine whether thereare irregularities in the prostate using the data acquired and, if so,to produce an indication of the locations of the irregular regions suchas by marking the regions on the prostate image. To further reveal areasin the prostate that are suspicious and require more detailedexamination, a second reference image can be simultaneously displayed.The reference image can be a computer simulated ideal normal prostate oran image of the prostate of the same patient obtained in a previousexamination. FIG. 20E illustrates a typical split screen display showingthe calculated model and reference model in the right-hand portion ofthe computer display along with the operator directive: "Examine areasof increased hardness".

The next step, which is optional, is to use the probe to furtherpressure map the regions of irregularity and transmit the additionaldata to the processor. Based on the differences between the examined andthe referenced prostates, the operator makes a decision on thedesirability of collecting additional data in the regions of interest.Such collection may take an additional 1 or 2 minutes, after which theoperator can terminate the examination as by pressing the "End of task"button and removing the probe from the patient.

In the final step, the computer calculates a virtual pressure patternsimilar to that shown in FIG. 14B preferably using all the datacollected. Then based on this virtual pressure pattern, the computercalculates a three-dimensional mechanical model of the prostate andfinally, it generates a three-dimensional image of the examinedprostate. It displays the examined prostate and preferably displays areference prostate. An additional advantageous feature is the ability torotate the image of the reconstructed prostate on the screen, as byusing an associated computer mouse. The computer can synchronouslyrotate the reference prostate to facilitate comparison and detection ofabnormalities.

The preferred method of preparing a three-dimensional image of theprostate can be better understood by considering the data flow chart ofFIG. 21. The first set of data in block A is actual data collected bythe probe. It constitutes a flow of real time force measurements fromthe pressure sensors and position measurements from the position sensor.In the most general case, it involves six position parameters (3coordinates of the position sensor and 3 angles describing the tilt ofthe probe tip) and pressure data from every pressure sensor.

The set of actual data is processed to a set of transformed data shownin block B of FIG. 21. By elementary geometrical processing, the actualposition data permits determination of three spatial coordinates foreach pressure sensor. Thus, one can relate every measured force valuefrom each sensor to a point in three-dimensional space. The forcemeasured by the sensor and its three coordinates are the transformeddata.

The transformed data can now be processed to provide pressure field datashown in block C. The transformed data contains both useful informationabout parameters of the tissue being investigated and noise of variousorigins. The noise originates from force and position measurement errorand from artifacts related to tissue movement (movement of the prostate,movement of the patient). Pressure field data is calculated byprocessing the transformed data to minimize noise and extract the 3Dspatial distribution of pressure approximating ideal conditions ofmeasurement. While there are a number of possible algorithms for thisprocessing, the preferred approach is to use Chebyshev approximation(polynomial approximation from Chebyshev coefficients) as described byJ. P. Boyd in Chebyshev and Fourier Spectral Methods, Springer Verlag(New York, 1989) and presented in algorithmic form by W. H. Press etal., Numerical Recipes in C, pp. 190-198 (Cambridge U. Press, 1996),both of which are incorporated herein by reference. The pressure fieldis represented as a superposition of Chebyshev polynomial functions.

The pressure field data can be processed to provide data on the geometryof the prostate surface and force gradients shown in block D. Havingapproximated (above) smooth surfaces of equal pressure, one cancalculate geometrical parameters and hardness of the prostate. Thesurface of the examined prostate can be obtained by choosing a level offorce corresponding to deformation of the rectal wall that permits thesensors to press against the prostate surface. From the pressuregradients, information on the prostate tissue hardness can be generated.

From the pressure field data approximated by Chebyshev polynomials, onecan now reconstruct a three-dimensional elasticity model of theprostate--a model which will show the distribution of hardness inthree-dimensional space. While there are a number of ways of calculatingthis model from the pressure field, the preferred method is 3Dreconstruction based on the finite element method described by G. Stranget al., An Analysis Of The Finite Element Method (Prentice Hall, 1973)and D. S. Burnett, Finite Element Analysis: From Concepts ToApplications (Addison-Wesley, 1987), both of which are incorporatedherein by reference.

A convenient way to produce an image from the calculated model is tostore an image of an ideal prostate and to deform the ideal image toconform to the calculated model using image modification techniques wellknown in the art. Advantageously, irregularities can be indicated on theimage to assist diagnosis.

In traditional medical imaging, the device usually displays thestructure of an object in terms of some measured physical property. Theimage obtained this way is often very far from what the actual examinedregion of body or an organ would look like if exposed to directsunlight, or drawn by an artist. Therefore, an expert in a particulartype of image analysis is required to tell the physician whatinformation from the image is relevant to the diagnosis. Currently, as aresult of a wider use of powerful computer means and databases, analternative approach to imaging, so called Knowledge-Based Imaging(Sarvazyan et al., A new philosophy of medical imaging, MedicalHypotheses 36, 327-335, 1991, incorporated herein by reference) hasstarted to emerge. The method of the present invention includes the useof the knowledge-based approach briefly described below. Usingknowledge-based imaging, a computer can store in memory a 3D picture ofa "normal" prostate which is being examined, and adjust (transform) thisimage according to the measured data, to produce an image thatrepresents the actual examined gland. Such a pictorial 3D image or itscross sections will additionally include data on the mechanicalproperties of the prostate. It will be significantly easier for aphysician to recognize abnormalities of the examined organ, representedon such an image. Further, the expert system will use the knowledgeabout characteristics of different types and stages of prostate cancerto point out any poorly defined and suspicious regions in the model, orjust show any abnormalities or deviations from what the "normal"prostate should look like. At this point, the physician can also enterinto the computer new information based on other tests or examsperformed on the same prostate, and the knowledge base will "learn" and"expand."

Once a 3D model of the actual examined prostate is stored in thecomputer, it must be presented by the user in a way that would allowboth external and internal features to be seen on one picture. Thismeans that the 3D image on the screen should contain information aboutgeometrical features of the prostate as well as spatial distribution ofelasticity and surface texture information. Additionally, the imageshould indicate to the user which areas of the examined prostate arepoorly defined and need to be examined further in order to produce acomplete diagnosis. There are several potential 3D visualization methodsthat can be suitable for this task, such as polygon based surfacemethods, ray cast volume rendering and cross section slicing.

Although certain presently preferred embodiments of the presentinvention have been specifically described herein, it will be apparentto those skilled in the art that variations and modifications of thevarious embodiments shown and described herein may be made withoutdeparting from the spirit and scope of the invention. Accordingly, it isintended that the invention be limited only to the extent required bythe appended claims and the applicable rules of law.

I claim:
 1. A transrectal probe for measuring mechanical properties ofthe prostate gland comprising:a control handle; a probe shaft having anaxis, said shaft extending from said handle; and a tip at the end ofsaid shaft for pressing against tissue overlying surfaces of theprostate gland, said tip comprising a position sensor for measuring theposition of said tip and an array of force sensors for measuring apattern of pressure when said tip is pressed against said tissue.
 2. Thetransrectal probe of claim 1 wherein the tip is movable above and belowthe axis of said probe shaft.
 3. The probe of claim 2 wherein said tipis covered by a disposable sheath of soft, flexible material.
 4. Theprobe of claim 2 wherein said tip and at least a portion of said shaftis covered by a disposable sheath of soft, flexible material.
 5. Theprobe of claim 1 further comprising paths for transmitting signals saidfrom said position sensor and the pattern of pressure detected by saidarray to a signal processor.
 6. The probe of claim 5 wherein saidcontrol handle comprises a switch for controlling input from saidposition sensor and said array of force sensors to a computer interface.7. The probe of claim 1 wherein said control handle comprises a pistolgrip handle.
 8. The probe of claim 1 wherein said force sensors comprisebending beam force sensors.
 9. The probe of claim 1 wherein said arrayof pressure sensors is formed of a left row of said pressure sensors anda right row of said pressure sensors, said left row of said pressuresensors measures pressure applied against the left surface of said tipand said tip and said right row of said pressure sensors measurespressure applied against the right surface of said tip.